(IEEESpectrum) Eleven researchers published their work on entangling a tardigrade on December 15 in the online preprint server arXiv, which is not peer-reviewed. Among them are Rainer Dumke of the Center for Quantum Technologies, in Singapore, and Tomasz Paterek of the University of Gdansk, in Poland, who in 2019 were honored, so to speak, with an IgNobel Prize for their work on magnetized cockroaches (the results of which bear on methods by which animals navigate).
Dumke and his colleagues came on their current interest in the course of studying superconducting qubits. They wondered what would happen if they put a dormant tardigrade on top of one of their qubits, bringing the system to near absolute zero.
First, they learned, the tardigrade survived. That alone is a significant finding. To entangle a life form you have to put it in an extreme vacuum and cool it nearly to absolute zero without killing it. Bacteria have been so entangled. Now a group of scientists say they’ve entangled a tardigrade, commonly called a water bear, a cute critter that’s just barely visible to the naked eye.
A tardigrade is a good candidate for freezing down to zero in a near-total vacuum. It’s about as tough as an animalcule gets. Insult the thing and it goes dormant by curling up into a ball, called a tun, in a process known as cryptobiosis. Though some have argued that at least some metabolism must still go on, a tun is perhaps best characterized as a life that’s been put on hold.
The presence of two superconducting qubits beside the tardigrade strengthens the case for the existence of entanglement—here it appears the creature is in superposition with one |0> qubit and one |1> qubit. The workers tested the system under a number of different conditions to determine the quantum state, and they found that the system consisting of the qubit and the tardigrade together occupied a lower energy state than either one alone would have occupied. The researchers concluded that the two things had been entangled.
No need to wait for peer review; in a matter of days, the criticism began to come in.
One critic, Ben Brubaker, a physicist turned journalist, has argued on Twitter that the experiments do not demonstrate what the authors claim
Vedral, another author, who is a professor of physics at the University of Oxford pointed out, “But the major weakness that there is no direct measurements on the tardigrade alone. This is what need to do to satisfy even the most conspiratorial critic, the one who says we could explain this with classical arguments.”
Kai Sheng Lee, of Singapore’s Nanyang Technological University, says that the criticism of the entanglement claim is at least partially answered in the second part of the arXiv paper, “when we introduce the second qubit.” The presence of two superconducting qubits beside the tardigrade strengthens the case for the existence of entanglement. . .”